1. Field of the Invention
The present invention is generally related to systems for the control of the temperature within a refrigerated space, and is more particularly related to a refrigeration temperature control system utilizing multiple sensors.
2. Description of the Prior Art
It is known in the art to control the temperature of a space used to store or transport perishable materials, such as foodstuffs. In controlling temperature in such a space, it is most difficult when the space is used to transport the perishable materials such as with refrigeration trucks.
Much of the difficulty arises because of the change in thermal loading caused by large changes in the ambient with respect to time of day, geographical location, and weather conditions. If the temperature within the refrigerated space becomes too high, the cargo is exposed to excess risk of spoilage. If the temperature within the refrigerated space becomes too low, portions of the cargo may be destroyed from freezing.
U.S. Pat. No. 4,715,190 discusses a rudimentary temperature control system. An advanced microprocessor based temperature control system is taught in U.S. Pat. No. 4,663,725, issued to Truckenbrod et al., and incorporated herein by reference. The Truckenbrod et al., system employs temperature sensors for the return and discharge of air. A fault recovery algorithm permits the system to switch between sensors. U.S. Pat. No. 4,589,060, issued to Zinsmeyer, also discusses a microprocessor based temperature control system.
Techniques for control of the refrigeration process are described in U.S. Pat. Nos. 4,742,689 and 4,934,155, issued to Lowes. These Lowes references show control of temperature through the use of hot gas bypass of the compressor in an attempt to maintain a more constant compressor speed.
A highly sophisticated system for temperature control is taught in U.S. Pat. No. 4,918,932, issued to Gustafson et al., and incorporated herein by reference. This system uses an integrated average of the outputs of a discharge sensor and a return sensor to control the refrigeration apparatus.